1. Field of the Invention
This invention pertains to hydraulic presses in the medium to high tonnage range, and particularly to those presses employed to exert very high forces over a small area as required, for example, in the processing of industrial diamonds.
2. Discussion of the Prior Art and Problems
Generally, the function of a hydraulic press is to provide a structure within which high forces are exerted upon a tooling or die assembly containing parts or materials to be processed, produced, or changed in size or shape. Such presses ordinarily include a force member, e.g., hydraulic ram or piston with an attached platen opposed by a resisting member known as a press crown or top head. Both the force and resisting member are retained in their relationship to each other by a number of columns, or by a housing frame of tie rod combinations.
The columns or tie rods normally extend through bores in the cylinder and press crown and are tightened by a nut at each end to a level which equals or exceeds the full tonnage of the press. This is called preloading and, while minimizing stress fluctuations, provides rigidity in this condition to prevent the separation of "parts" during the pressing cycle. The reduction of movement under load generally increases the life of "parts". The "parts" referred to above are within a tooling apparatus, i.e. die assembly or the like, and consist of several mating elements which are tailored for a specific application. The elements of the tooling apparatus are normally attached to both the press crown and platen through which the cylinder will exert its force, close the elements about a material, and produce a useful item.
The press crown can be considered a beam fixed between two or more points, i.e., the columns or tie rods. The distance between the points is called the span. The amount of deflection induced into the press crown is a function of its span, the force imparted by the force member, and the depth of the press crown. For a given span and force, i.e. load, the deflection can be varied only by a significant change in the depth of the press crown. Thus, if it were desired to decrease the deflection induced by a specific load, the depth or vertical section of the press crown between the fixed points would have to be increased by a considerable amount. A practical problem then results, since the increased depth of the press crown adds considerable weight and, therefore, cost to the entire press assembly.
When employing presses in applications requiring close tolerances, it is absolutely imperative that the deflection in the press crown, which adversely affects the adjoining tool package by imposing additional lateral forces, be minimized. For example, in ultra high load applications, it is necessary to use tungsten or similar materials as the tooling composition to resist the pressures and temperatures. Tungsten, however, like many materials with a high Young's Modulus has poor bending ability. Where precise mating of die assemblies in the tooling apparatus is a requirement, relative lateral movement of one die to the other could add additional stresses and result in premature failure.
It is therefore one object of the present invention to provide for a press assembly with a press crown which will resist and complement the hydraulic forces transferred through the tooling apparatus. Another object of this invention is to provide a press crown with a shape which transfers a significant amount of deflection to a portion of the press crown outside of the region above the tooling apparatus. Still another object is to provide a press crown with a transitional region connecting its center to the portions receiving the columns or tie rods, which regions will minimize bending of the columns or tie rods in the preload condition.